PT - JOURNAL ARTICLE AU - Misty R. Riddle AU - Fleur Damen AU - Ariel Aspiras AU - Julius A. Tabin AU - Suzanne McGaugh AU - Clifford J. Tabin TI - Evolution of the gastrointestinal tract morphology and plasticity in cave-adapted Mexican tetra, <em>Astyanax mexicanus</em> AID - 10.1101/852814 DP - 2019 Jan 01 TA - bioRxiv PG - 852814 4099 - http://biorxiv.org/content/early/2019/11/23/852814.short 4100 - http://biorxiv.org/content/early/2019/11/23/852814.full AB - The gastrointestinal tract has evolved in numerous ways to allow animals to optimally assimilate energy from different food sources. The morphology and physiology of the gut is plastic and can be greatly altered by diet in some animals. In this study, we investigate the evolution and plasticity of gastrointestinal tract morphology by comparing laboratory raised cave-adapted and river-adapted forms of the Mexican tetra, Astyanax mexicanus reared under different dietary conditions. In the wild, river-dwelling populations (surface fish) consume plants and insects throughout the year, while cave-dwelling populations (cavefish) live in a perpetually-dark environment dependent on nutrient-poor food brought in by bats or seasonal floods. We find that multiple cave populations converged on a reduced number of digestive appendages called pyloric caeca and that some cave populations have a lengthened gut while others have a shortened gut. Moreover, we identified differences in how gut morphology and proliferation of the epithelium respond to diet between surface fish and cavefish. Using a combination of quantitative genetic mapping, population genetics, and RNA sequencing we implicate molecular and genetic changes influencing cell proliferation, cell signaling, and immune system function in the evolution of gut morphology.